1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
In the field of electrophotography, recently, high quality images such as color images have been formed. Formation of such color images increases halftone images and solid images, leading to a demand for improved image quality. For example, in the case where a reversal development type electrophotographic apparatus is used to form an image in which a portion in one image irradiated with light becomes a halftone image in the next rotation, a phenomenon (positive ghost phenomenon) is likely to occur, i.e., only the density of the portion irradiated with the light is increased.
One type of the electrophotographic photosensitive member includes a charge-generating layer comprising a charge-generating substance (organic photoconductive substance) and a hole-transporting layer comprising a hole-transporting substance, the layers being provided on a conductive support. Other type of the electrophotographic photosensitive member includes a single layer photosensitive layer comprising a charge-generating substance and a hole-transporting substance and provided on a conductive support.
Unfortunately, if only the photosensitive layer is provided on the conductive support, hole injection may be caused from the conductive support to the photosensitive layer at the time of applying voltage to the electrophotographic photosensitive member. Hole injection from the conductive support to the photosensitive layer causes image defects of black dots (black spots) to remarkably reduce the image quality.
In order to suppress production of the black spots, there is a method in which the so-called intermediate layer having electrical blocking function is provided between the photosensitive layer and the conductive support.
On the other hand, if the electrical resistance of the intermediate layer is excessively high, electrons produced in the charge-generating layer stagnate within the photosensitive layer to cause the ghost phenomenon. Accordingly, the electrical resistance value of the intermediate layer needs to be small to some extent, and both improvement of the ghost and suppression of the black spots are required.
Then, there is a method in which a metal-oxide particle is included in the intermediate layer in order to suppress stagnation of the electrons within the photosensitive layer and improve the ghost in the electrophotographic photosensitive member. Unfortunately, hole injection from the conductive support to the photosensitive layer is undesirably promoted to produce the black spots while the ghost is well improved by reduction in the electrical resistance value of the intermediate layer.
Then, in order to improve the ghost and suppress the black spots, Japanese Patent Application Laid-Open No. H03-013957 proposes that a metal-oxide particle surface-treated with an organic titanium compound is included in the intermediate layer. Moreover, Japanese Patent Application Laid-Open No. 2005-292821 proposes that a metal-oxide particle surface-treated with a reactive organic compound containing sulfur atoms is included in the intermediate layer. Further, Japanese Patent Application Laid-Open No. 2005-037480 proposes that a metal-oxide particle surface-treated with a reactive low molecular organic silicon compound is included in the intermediate layer. Japanese Patent Application Laid-Open No. 2008-299020 proposes that a metal-oxide particle surface-treated with a reactive polymeric organic silicon compound is included in the intermediate layer.
However, any of the intermediate layers each including the metal-oxide particle subjected to the corresponding surface treatment cannot improve the ghost and suppress the black spots at a high level.